Determination of certain metals is of value in a variety of industries. Quantitative determinations of metals plays a role in commercial industries as well as in environmental studies. Two such metals of interest are nickel and cobalt. It is particularly useful to quantitatively determine the presence of nickel and cobalt in protein solutions, such as in biological materials.
There are many determination methods reported in the prior art. One commonly used method is to detect nickel by colorimetric means, such as where a nickel sample is analyzed by spectroscopy. The most well known and widely used colorimetric method of determining nickel is the dimethylglyoxime test. This test has been used for many years, however, it has major drawbacks. The test is time consuming and inconvenient, and excess reagent may precipitate thereby adversely affecting the results of the test. Moreover, many metal ions interfere with this procedure, and a series of chloroform extractions, followed by ammonia and hydrochloric acid washes are necessary to remove the metal ions and prevent interference.
Another method for colorimetric, or spectrophotometric, determination of nickel in biological materials uses .alpha.-furildioxime as the reagent. This method differs from the dimethylglyoxime procedure only in the reagent used; this test has all the problems of the aforementioned method, and is only useful over a very narrow concentration range of nickel (0.5 to 4.0 ppm nickel).
Many other methods for the colorimetric determination of nickel are reported, however all of these methods exhibit significant limitations. Some are excessively slow or overly narrow. Others require hazardous solvents or involve reagents which must be synthesized in the laboratory. Some methods measure wavelength in the ultraviolet range where common detergents may cause interference. And further, many techniques require very large sample sizes of up to 200 ml and rely on preconcentration techniques to achieve their sensitivity.
Another limitation of prior art methods, is their susceptibility to interference from other metals. The presence of other metal ions, especially cobalt, interfere with the determination of nickel. Extraction techniques are required to remove the interference, and some techniques are quite elaborate such as using anion exchange chromatography to remove interference from cobalt, copper and iron as described by Scoggins, M. W., Analytical Chemistry, v. 42, p 301-3.
It is known that nickel forms colored compounds when reacted with certain thiolates. For example, dithizone has been used to determine nickel by colorimetric means. However, this method requires extraction techniques using chloroform which make this process no better than the other prior art techniques. Another thiolate compound, namely 3-thiobenzoyl-1-p-tolylthiocarbamide, has been reported as a reagent for colorimetric determination of both nickel and cobalt in Ambhore, D. P. and Joshi, A. P., Indian Journal of Chemistry, v. 25, p 699-700; but again, this technique requires extractions and the thio compound must be synthesized in the laboratory.
Thus, it is highly desirable to provide a method and reagent capable of providing a rapid and accurate determination of nickel and cobalt, that operates over a wide range of concentrations, is not suspectable to interference from other metal ions and is free from cumbersome extraction techniques.